Recently, aqueous paints containing only a very small amount of organic solvent or no organic solvent have been increasingly used in the field of paints to save resources and prevent environmental pollution.
Further, a high grade finish which has been conventionally achieved only with a solvent type paint can be achieved with an aqueous paint due to the remarkable technical development of resins for aqueous paints. In a metallic paint containing various metal powder pigments such as an aluminium pigment, however, very few examples of aqueous paints can be practically used. In particular, no example of practically applicable aqueous paints can be found in a metallic paints which can be used for the coating of automobiles and electrical home appliances which require a high grade finish of a coated film and high durability thereof.
One of the reasons of the above mentioned disadvantage is that various metal powder pigments including the aluminium pigment ar liable to erosion in aqueous paints. In particular, when metal powder exists in aqueous paints, metal erosion is caused by water in a pH range of from acidity to basicity based on the nature of various metals, and hydrogen gas is generated accordingly. The hydrogen gas generation is a very serious problem in the paint making process of paint manufacturers and in a coating process used by manufacturers of automobiles and electrical home appliances from the view point of safety. Note that references to the storge stbility of the metal powder pigment in this specification and appended claims pertain to both the erosiveness of a metal powder pigment in an aqueous paint and the erosiveness of a metal powder pigment when it is independently stored without being prepared as a paint.
Although many inventions have been disclosed up to now to improve this storage stability, no practically applicable technologies have been yet established. For example, in order to improve the storage stability of a metallic powder pigment, a method of using a wetting agent such as polyamide, aliphatic amide, fluorine, silicone and the like, is disclosed in U.S. Pat. No. 3,893,254, a method of using a perfluoroalkyl type wetting agent is disclosed in U.S. Pat. No. 3,926,874, and a method of using a fatty acid or a fatty acid alkanol amide with a nonionic wetting agent is disclosed in U.S. Pat. No. 4,138,270. None of these methods, however, exhibits a sufficient effect for improving the storage stability. Furthremore, such methods have a problem in that the metal powder pigment shows a poor wetting property with water.
Further, a method of using caprolactone phosphoric acid ester is disclosed in Japanese Patent Application Kokai (Laid-Open) No. Sho 61 (1986)-298072 for the purpose of improving storage stability by restricting the reaction of a metal powder pigment with water. A method of using octylphenyl dihydrogen phosphate and diethylamine adduct of bis(octylphenyl) hydrogen phosphate is disclosed in Japanese Patent Application Kokai No. Sho 60 (1985)-15466 for the same purpose. A method of using a reaction product of orthophosphoric acid or phosphoric acid monoester with an epoxy compound in an aqueous paint is disclosed in Japanese Patent Application Kokai No. Sho 61 (1986)-47771. A method of using a reaction product of styrene allyl alcohol copolymer, p-tert-amylphenol with orthophosphoric acid or phosphorus pentaoxide as an aqueous paint is disclosed in Japanese Patent Application Kokai No. Sho 61 (1986)-291662. None of these methods, however, can be practically applied because they do not show sufficient improvement. The storage stability provided by these methods is not sufficient when stored in the form of a metal powder pigment as only a relatively small improvement can be observed, and the metal powder pigment which can be stored only in the form of a paint by such methods.
The applicant herein discloses a very effective method of restricting the erosive reaction of the metal powder pigment with water by using a specific organic phosphoric acid ester disclosed in Japanese Patent Kokoku (Post Exam. Publication) No. Sho 60 (1985)-8057. However, it is found that when the compound disclosed in that document is used in a metal powder pigment which is applied to an aqueous paint, in particular, to an aqueous metallic paint used for the facing of automobiles and electric home appliances, the performance of the resultant coated film cannot always meet all the required characteristics. One of the reasons of the above is that, as the application fields of aqueous paints expands, the level of the requirements from the users become more demanding. The following two aspects would be the cause behind such a demand. First, a finished appearance which is equal or superior to that obtained by a solvent type paint, which has been conventionally impossible, becomes possible even with an aqueous paint as mentioned above; and second, the aqueous paint is to be a most-likely candidate capable of meeting social requirements such as regulation on the use of solvent and saving of resources. In particular, there exist a strong demand for replacing high grade finish solvent type metallic paints, which have a very high content of organic solvent therein, with aqueous metallic paint.